1. Field of the Invention
The present invention relates to a semiconductor laser apparatus for an optical head for performing laser beam radiation and incident laser beam detection.
2. Description of the Prior Art
An optical head used in an optical recording/reproducing system or the like irradiates an optical recording medium with a light beam, and detects a modulated light beam from the optical recording medium to perform information recording/reproducing.
The optical head normally uses a semiconductor laser apparatus. Namely, a laser light beam radiated from a semiconductor laser and reflected by a beam splitter is incident on an optical recording medium through an objective lens. The beam, reflected by the optical recording medium and passing through the objective lens and the beam splitter, is incident on a photodetector.
In the optical head, the semiconductor laser, the beam splitter and the photodetector constitute a semiconductor laser apparatus. In the conventional semiconductor laser apparatus, positional adjustment of the three separate optical components results in a high cost for the optical head.
The assignee of the present application filed a patent application on Apr. 17, 1986 to the U.S. Patent Office, entitled "Semiconductor laser apparatus" and identified as Ser. No. 853,210, now U.S. Pat. No. 4,733,067 which solves the above-mentioned problem. The semiconductor laser apparatus disclosed in this U.S. Pat. No. 4,733,067 is such that a laser diode as a light source and a plurality of photodetectors for detecting a light reflected by an optical disc are formed on a semiconductor substrate. Further, on the semiconductor substrate, there is fixed a prism positioned above the photodetectors for introducing the reflected light from the optical disc to the photodetectors.
The semiconductor laser apparatus as mentioned above has the laser diode as a light source, the respective photodetectors, the prism and so on formed on the same single semiconductor substrate so that it is possible to reduce the size of the optical head as well as simplify its structure, to thereby largely reduce the production cost thereof. However, a stray light incident from a semitransparent reflecting plane, that is, a direct light from the laser diode is incident on the photodetectors so that the detecting sensitivity of the photodetectors is decreased and the detecting error is increased.